Is there a blood-brain barrier at the optic nerve head?
M. O. Tso, C. Y. Shih and I. W. McLean
The retina and optic nerve have been demonstrated to possess a blood-brain
barrier that prevents the passive passage of protein and certain dyes from
the blood vessels into the extracellular space. Our observations suggest
that an exception is present at the normal optic disc. Using horseradish
peroxidase as a tracer for electron microscopy and the normal rhesus monkey
as the experimental animal, we have demonstrated that in certain regions of
the optic nerve head, horseradish peroxidase from the blood stream reaches
the axons of the optic nerve through the border tissue of Elschnig from the
adjacent choridal tissues. A barrier formed by a series of cell junctions
between glial cells at the edge of the optic disc prevented spread of the
tracer from the optic disc into the subretinal space.
